Unit dose dispensers, or dispensers having metering valves that discharge predetermined volumes of liquefied formulation, are known in the art. Where the formulation includes medication for certain specific purposes, such as a medication for use in the nasal passages, a metering valve that discharges fixed volumes of medication at each discharge is desired. Several such valves are disclosed in the following references: U.S. Pat. No. 4,892,232; U.S. Pat. No. 5,105,995; U.S. Pat. No. 5,085,351; U.S. Pat. No. 5,183,187; U.S. Pat. No. 5,484,088; U.S. Pat. No. 6,695,175 B2; and U.S. Pat. No. 6,910,606 B2. Existing metering valves discharge liquefied formulation from a pressurized container that is filled either prior to attaching the valve at the upper end of the container, or through a port at the bottom of the container; however, it is often desirable to fill the formulation through the metering valve. For example, formulations that include an evaporant such as needed to create a mist or foam are retained in a bag within the container, with the bag surrounded by a propellant. The propellant pressurizes the bag and thereby retaining the liquefied gas in its liquid state.
It should be noted that existing adjustable metering valves are not suitable for discharging a formulation that includes a liquefied gas that is retained in liquid form by the propellant. This is because the liquefied evaporant turns to gas as soon as the valve opens the metering chamber to the ambient thereby causing all the formulation in the metering chamber, not just the portion adjacent a moveable metering wall, to be discharged trough the valve. However, unit dose valves that are not adjustable can discharge a fixed amount formulation, including an evaporant, on each depression of a the valve actuator.
In order for such a metering valve to discharge a formulation that includes a liquefied gas, the formulation must be maintained under pressure while it is being inserted into a bag within the container. The bag must therefore have a single port through which the contents thereof are both filled and discharged. That is, the bag must be filled through the dispensing valve which extends into the bag. All metering valves release a predetermined volume of formulation on each actuation do not permit the filling of the formulation through the stem of the valve.
Beard, U.S. Pat. No. 3,104,785 discloses a metering valve that can be filled through the stem of the valve and discharges a fixed amount of formulation on each actuation; however, Beard requires that the dispensing stem be in a depressed condition at the time the liquid is filled through the metering valve. There is therefore a need for an improved metering valve that dispenses a fixed volume of formulation on each actuation and through which the container can be filled.